1. Field of the Invention
The present invention relates to a process for producing a non-woven fabric of ultrafine polyolefin fibers by subjecting a web of splittable conjugate polyolefin fibers to a water needle processing, and non-woven fabrics having a good hydrophilic property, softness, and wiping property, and being obtained from the splittable composite fibers.
2. Description of the Related Art
Recently, woven or non-woven fabrics comprising ultrafine fibers are widely used from the aspect of their excellent softness, hand feeling, and wiping property, and their high strength. As the methods for producing the woven or non-woven fabrics, a method is generally performed in which multi-core type composite fibers, so called "sea-island type composite fibers", produced from two or more kinds of resins having a different solubility are converted into a fabric through a process for weaving, and then the sea component is removed to form a woven fabric of ultrafine fibers (Japanese Patent Publication No. Sho 43-7411). Alternatively, a method is conducted in which composite fibers, so-called "splittable composite fibers", in which two or more components having a low solubility to each other are adhered are converted into a web by a dry or wet method, and then subjected to a process for splitting and entangling of fibers with a mechanical impact such as one with a jet of high pressure water streams to obtain a non-woven fabric of ultrafine fibers (Japanese Patent Publication No. Sho 48-28005, Laid-open WO Japanese Patent Publication No. Hei 5-321018, and Japanese Patent Publication No. Hei 6-63129).
However, the method employing sea-island type composite fibers has such a problem that the method needs a step for weaving and a step for dissolving a component of the composite fibers, and thus the steps for producing a fabric becomes complicate as a whole.
On the other hand, according to the method employing splittable composite fibers, a non-woven fabric of ultrafine fibers is readily obtained, related to the method mentioned above, by subjecting the web obtained, for example, by a carding process to splitting and entanglement of fibers at the same time with high pressure water streams. However, the resins which form the splittable composite fibers must be readily splitted by a mechanical impact (or shock) and thus they are selected from the different kind of resins having a low solubility to each other. For example, a couple of resins selected from the group of polyamides, polyesters, and polyolefins are preferably used. Accordingly, splitting occurs in the midst of steps when webs are formed through steps including a carding step in a dry method.
General synthetic fibers are usually applied with a surface active agent on their surface for the purpose of suppressing generation of static electricity during processing steps. However, as the splitting mentioned above progresses, the surface area of the fibers increases and static electricity is generated, leading to a considerable deterioration of card passability of the fibers. When a fiber finishing agent was additionally applied at a carding step to suppress generation of static electricity, such problems as contamination of carding machines and lowering of web strength occur.
With conventional splittable composite fibers, a hydrophilic surface active agent which had been applied on the fiber surface as fiber finishing agent is rapidly washed away with high pressure water streams at a step for forming a non-woven fabric. On the other hand, polyolefin resin represented by polyethylene is extremely high in hydrophobic property such that its official water regain is 0%. Thus, the fibers from polyolefin avoid water stream at an initial stage of step using high pressure water streams for forming non-woven fabrics, and thus the fibers can not uniformly receive the impact energy with water. Accordingly, non-woven fabrics of ultrafine fibers splitted uniformly to a sufficient extent can not be obtained unless the number of steps using the high pressure water streams is increased.